Aromatic diamines having two amino groups in one molecule have been used as a surface protection film or an interlayer dielectric film of semiconductor elements and as a raw material for polyamide resins having excellent heat resistance and outstanding electric and mechanical properties, and particularly as a raw material for a polyimide resin.
In recent years, due to an increase in demand for high-performance semiconductor elements, a resin having higher reliability is desired. A polybenzoxazole resin in which bis(aminophenol) is used as one of the raw materials has begun to be used in the latest semiconductor elements as a material having moisture-proof reliability due to non-possession of a carbonyl group derived from a high polar imide ring.
A part of a patterning process can be simplified by providing these resins with photosensitivity. A photosensitive resin composition having an effect of reducing the process time and increasing the yield is being developed by using these resins. More recently, a positive-type photosensitive resin composition which can be developed using an alkaline aqueous solution has been developed from the viewpoint of safety. For example, Patent Document 1 discloses a positive-type photosensitive resin composition which comprises a polybenzoxazole precursor having a structure derived from a bis(aminophenol) compound and dicarboxylic acid as a base resin and a diazoquinone compound as a sensitizer. The composition has high heat resistance, outstanding electrical properties, and fine patterning ability and has a possibility of being used not only as a wafer coating material, but also as a resin composition for interlayer insulation.
The development mechanism of the positive-type photosensitive resin composition is as follows. The diazoquinone compound in the unexposed area is insoluble in an alkaline aqueous solution. The base resin is provided with resistance to the alkaline aqueous solution as a result of an interaction with the diazoquinone compound. On the other hand, if exposed to light, the diazoquinone compound chemically changes and becomes soluble in an alkaline aqueous solution, and promotes dissolution of the base resin. A coated relief pattern consisting only of the resin composition in the unexposed area can be prepared by removing the exposed area by dissolution using the solubility difference of the exposed area and unexposed area patterning. The polybenzoxazole precursor resin in the positive-type photosensitive resin composition from which the coated relief pattern has been formed is cyclized by dehydration when cured at a temperature of about 300° C., whereby the precursor resin ultimately turns into a polybenzoxazole resin having high heat resistance. Remarkable miniaturization and high integration of semiconductor elements in recent years have reduced heat resistance, particularly of storage elements. In order to increase the yield of semiconductor elements, a polybenzoxazole precursor resin which can be cured at a lower temperature is demanded. The cyclization rate of the resin after curing is an important factor when curing the resin at a low temperature. A low cyclization rate not only lowers the moisture-proof reliability and chemical resistance due to an increase in the moisture absorption rate owing to the effect of alkali-soluble groups remaining in the resin, but also increases the dielectric constant.
In an effort to increase the cyclization rate, Patent Document 2, for example, discloses a polybenzoxazole precursor resin in which bis(aminophenol) containing an ether bond is used. The bis(aminophenol) containing an ether bond causes the molecular chains to move easily. Pattern formation using the polybenzoxazole precursor resin, however, is difficult because the polybenzoxazole precursor resin exhibits only very low transparency to ultraviolet radiation with a wavelength of 365 nm (i-line) which is very frequently used as an actinic rays in an exposure process.
When a positive-type photosensitive resin composition is used in practice, the sensitivity of the photosensitive resin composition is particularly important. Low sensitivity requires a long exposure time, which results in a low throughput. In order to increase the sensitivity of the photosensitive resin composition, a method of protecting the phenolic hydroxyl group in the polybenzoxazole precursor resin using an appropriate organic group may be conceivable. This method controls the intramolecular hydrogen bonding and increase transparency to i-line. However, the resulting resin composition is not sufficiently dissolved in an alkaline aqueous solution since the phenolic hydroxyl group which is an alkali soluble group is protected. Not only is the sensitivity lowered, but also the resin can be cyclized only with difficulty because of the increased distance between the phenolic hydroxyl group and the carbonyl carbon of the amide group.
Therefore, development of a positive-type photosensitive resin composition using a polybenzoxazole precursor resin exhibiting high sensitivity and a high cyclization rate even if cured at a low temperature, that is, a resin composition which satisfies both processability and reliability when cured at a low temperature is strongly desired. That is to say, it has been difficult for a general positive-type photosensitive resin composition to satisfy both high sensitivity and high cyclization rate when cured at a low temperature by using a polybenzoxazole precursor resin.
[Patent Document 1] Japanese Patent Publication No. 1-46862
[Patent Document 2] Japanese Patent No. 3078175
As the resin used for a positive-type photosensitive resin composition, in addition to the polybenzoxazole precursor resin having a benzoxazole precursor structure, a polybenzoxazole resin having a benzoxazole structure, a polyimide precursor resin having an imide precursor structure, a polyimide precursor resin having an amide acid ester structure, and a polyimide resin having an imide structure can be given. The polyimide precursor resins easily dissolve unexposed parts. Not only is it difficult for the polyimide precursor resins to produce a coated relief pattern, but it is also difficult to increase transparency to i-line in spite of the properties as a protecting film and an interlayer dielectric film for semiconductor elements and display elements. The polyimide precursor resins thus have a drawback of low sensitivity. Another problem with the polyimide precursor resins is high water absorption of a cured film, which leads to impairing reliability. Furthermore, the polyimide resin has a problem of reducing sensitivity when the imide ring absorbs actinic rays. In addition, there is the same problem of high water absorption of a cured film and poor reliability as in the polyimide precursor resin.
The present invention has been achieved in view of this situation and has an object of providing a positive-type photosensitive resin composition containing a polyamide resin having a benzoxazole precursor structure, particularly a polyamide resin containing the benzoxazole precursor structure as a major component, exhibiting high sensitivity and a high cyclization rate even when cured at a low temperature, and also a polyamide resin used as a raw material of the positive-type photosensitive resin composition. Another object of the present invention is to provide a positive-type photosensitive resin composition containing a polyamide resin having a benzoxazole structure, particularly a polyamide resin containing the benzoxazole structure as a major component, exhibiting high sensitivity and a high cyclization rate even when cured at a low temperature, and also a polyamide resin used as a raw material of the positive-type photosensitive resin composition. Still another object of the present invention is to provide a positive-type photosensitive resin composition containing a polyamide resin having an imide structure, an imide precursor structure, or an amide acid ester structure, exhibiting high sensitivity and a low moisture absorption rate even when cured at a low temperature, and also a polyamide resin used as a raw material of the positive-type photosensitive resin composition. A further object of the present invention is to provide a bis(aminophenol) derivative used as a raw material for the polyamide resins. A still further object of the present invention is to provide a protective film and an interlayer dielectric film produced from the positive-type photosensitive resin composition and a semiconductor element and a display element in which the protective film and the interlayer dielectric film are used.